Recently, because of the exhaustion of petroleum resources, heavier crude oils have come to be used, thus giving rise to an increasing tendency of the amount of heavy oils by-produced such as residual oils in distillations. These heavy residual oils are of less industrial value by reason of their high viscosity or high sulfur and metal contents.
On the other hand, such heavy residual oils can be utilized in thermal cracking processes typified by coking, which may be the only utilization mode of those oils. From the heavy residual oil coking process is obtained a liquid substance, i.e., thermal-cracked oil , as well as coke and gas. Usually, the yield of the thermal-cracked oil in coking is fairly high, so there is obtained a large amount of thermal-cracked oil distillate.
Since the thermal-cracked oil thus obtained in a large amount contains a relatively large amount of aliphatic hydrocarbons and does not have a sufficiently high octane number, it has heretofore not been used directly as gasoline for automobiles, for which purpose it is required to be further subjected to a fluid catalytic cracking, for example. At most, it has been used merely as fuel for boilers. Therefore, how to utilize this large amount of thermal-cracked oil is becoming a serious industrial problem.
It has widely been conducted as what is called naphtha cracking to produce basic materials in the petrochemical industry such as ethylene and propylene by thermally cracking petrolic light hydrocarbons such as naphtha at 750.degree.-850.degree. C. In this case, 0.5 to 3.0 weight percent, based on the amount of ethylene produced, of thermal-cracked by-product oil containing a large amount of aromatic hydrocarbons is by-produced although the amount of this by-product oil differs depending on the kind of feed oil supplied to the thermal cracking apparatus, cracking conditions, etc.
Also, a reformate obtained in a large amount from a catalytic reforming also contains a large amount of aromatic hydrocarbons inevitably in which catalytic reforming naphtha is contacted with a noble metal catalyst such as Pt or Pt-Re/Al.sub.2 O.sub.3 in the presence of hydrogen in order to improve the octane number or increase the content of aromatic hydrocarbons such as benzene, toluene and xylene to obtain those hydrocarbons.
Further, the residual oil after separation and removal of benzene, toluene and xylene from the above thermal-cracked by-product oil or reformate by a separating means such as solvent extraction is a distillate which mainly contains aromatic hydrocarbons of C.sub.9 and C.sub.10. However, this distillate is a mixture of many components and has heretofore not been fully utilized industrially because the separation into each component is difficult as one reason.
It is an object of the present invention to effectively utilize thermal-cracked oil distillates from heavy residual oils which have not so far been fully utilized industrially. It is another object of the invention to attain an effective utilization of residual oil in a BTX manufacturing process which is not in a sufficient industrial utilization. It is a further object of the present invention to provide a surface active agent which is inexpensive and yet superior in performance.